Many mobile communication technologies are adopting an OFDMA scheme or a SC-FDMA scheme. In IEEE 802.16, 802.20 and Wibro systems that are applied to a portable Internet system, the OFDMA scheme is adopted as the standard. Standardization for a cellular system is made in 3 Generation Partnership Project (3GPP). 3GPP adopted the OFDMA scheme and the SC-FDMA scheme.
A communication system using the OFDMA scheme and the SC-FDMA scheme uses a cyclic prefix symbol. At this point, the length of the cyclic prefix symbol is designed longer than that of the impulse response of a channel for overcoming limitations caused by multipath fading. Accordingly, by using a single tap equalizer in a frequency domain, the distortion of an estimated channel is compensated. In this case, the accurate estimation of a channel is required for compensating the distortion of the channel.
In a mobile communication system having dispersed pilots, a channel estimation operation is performed using the dispersed pilots, and the channel between a plurality of data sub-carriers is estimated through the channel estimation operation. That is, a Least Square (LS) estimator estimates a channel with a pilot sub-carrier, and channel-estimated values, i.e., channels between the data sub-carriers are estimated in a linear interpolation scheme. In such a method, however, the maximum delay time of a wireless channel is long. In the estimation of a channel having high frequency selectivity, accordingly, channel estimation performance is degraded. For solving this, a channel estimation method in a time domain using a Fast Fourier Transform (FFT) scheme is applied.
The channel estimation method in the time domain changes channel-estimated values, in which the LS estimator has estimated channels for a pilot sub-carrier, into a time domain through an Inverse Fast Fourier Transform (IFFT) scheme. Subsequently, an N-point FFT operation is performed through an operation of extracting samples in which the power of a sample in a desired time domain exceeds a specific critical value, i.e., a gating operation. When the N-point FFT operation is completed, channel estimation in a pilot sub-carrier and a channel frequency response in a data sub-carrier position are acquired.
In a channel estimation method in a time domain, when the gating operation is completed, performance is improved in portions other than the both end regions (hereinafter referred to as an edge) of an IFFT input, irrespective of a frequency selectivity. However, channel estimation performance is degraded in the edge region of the IFFT input. This provides causes that further deteriorate the channel estimation performance by being added to the Gibbs phenomenon that occurs when a time domain is changed into a frequency domain.